(1) Field of the Invention
The present invention relates to image forming apparatuses such as printers, and in particular to an image forming apparatus that is orientatable in different positions.
(2) Related Art
Generally, an image forming apparatus such as a printer has a paper feed tray that assumes a substantially horizontal position when the apparatus is set up. In such an image forming apparatus, a pickup roller picks up one recording sheet at a time from a plurality of recording sheets stored in the paper feed tray and transports the recording sheet, on which an images will be formed.
Japanese Patent Application Publication No. 2006-298616 discloses a lifter designed for stable paper feeding. The lifter lifts up a sheet loading plate loaded with the recording sheets, so that the recording sheets are pressed against the pickup roller. The lifter includes: a first elastic member that rotates a turnable pressurizing plate by linear elastic force, the pressurizing plate lifting up the sheet loading plate; and a second elastic member that rotates the sheet loading plate by nonlinear elastic force. The first elastic member and the second electric member cause the pickup roller to apply paper feed pressure against the recording sheets loaded on the sheet loading plate.
Meanwhile, considering the space occupied by the apparatus in an office or home, research for developing an image forming apparatus that can be orientated not only in the horizontal position with the paper feed tray assuming a substantially horizontal position, but also in an upright position, which is the position raised up from the horizontal position by substantially 90° (e.g. Japanese Patent Application Publication No. H08-314333).
However, a conventional image forming apparatus orientated in the upright position often causes a paper feed failure such as multiple feed. Multiple feed is a problem that the apparatus cannot separate one recording sheet from the recording sheets loaded in the paper feed tray, and transports several sheets at a time.